Jump to content

Twin motor/esc/battery set up


Recommended Posts

As a short break from a balsa glider build I'm finally putting together a Mpx Twinstar that I've had for 5 years.

 

I know this has been discussed many times but I'd like thoughts on best practice between lengthening the wires between Motor to ESC v Battery to ESC.

This will dictate whether I mount the ESC's in the fuselage or on the wing directly behind the motor and need to make a decision before I go any further with the model.

 

Cheers.

 

Link to comment
Share on other sites

Hi,

The best practice is to follow manufacturers recommendations as some say you should not extent battery leads, some say extend with capacitors and others say its not an issue. IMO there seems to be less of an issue with extending motor leads.

 

Of course finding the relevant information might be harder form some suppliers hence why I use 4Max for non standard applications. Either email or best to phone George explain your application and purchase the necessary bits. If you do have an issue you can always give him a call and discuss. You pays your money and takes your choice and if you have the time and expertise you can get into the nitty gritty programming, but TBH I would rather be flying ?

 

PS I have 5 twins all with long battery to ESC leads and they all work just fine as there is plenty of cooling in the cowls.

Link to comment
Share on other sites

There has been much discussion about this.

The problem as best I have been able to determine is a matter of almost random failure due to voltage spikes.

The capacitors ahead of the input to the ESC are there to smooth out any voltage spikes which occur every time the ESC switched the amps from one pair of motor wires to the other. The spikes are small but smoothing them requires the capacitor to absorb energy and by doing so generates heat. Heat will eventually cause the capacitor to fail. Then the voltage spikes get through to the MOSFETs which will soon fail.

Obviously the size and frequency of the voltage spikes and the amps involved determines how much power the capacitor(s) have to absorb. You can't do much about the frequency and the amps as that is due to flying but adding to the battery ESC wire length will increase the size of each voltage spike.

So it comes down to a 'reliability' issue. One assumes by using the provided tails the chances of capacitor failure over time are suitably small but increasing the battery to ESC wire length will shorten the capacitors life by some factor but by how much is almost impossible to ascertain as there are many variables at play.

 

It is of course quite possible that even a shortened capacitor life will still be longer than the life of the model. ?

 

  • Like 1
Link to comment
Share on other sites

Hi Simon,

I have to disagree and hopefully if I explain you may see where I am coming from!

I don’t think they are random failures because:

·         Manufacturers recognize there is an issue because they give advice as in do/don’t/fit caps etc.

·         Chatting with George he explained that it was an issue and that the products were redesigned to eliminate the problem. However as we know other manufactures either advise caps or don’t recommend doing it

·         Some manufacturers will use the cheapest, low spec components available to sell a product just fit for purpose. If its stressed by poor cooling, long leads etc then it is far more likely to fail.

 

Yes the input caps are there, but IMO the fact that the battery is close and has a low internal resistance reduces the voltage spikes. Again if caps are used with lower voltage rating then its more likely they will fail and then stress the FET to the point of failure (especially if they are of a low voltage rating). If you use longer battery to ESC leads it puts greater stress on the capacitors from a peak voltage point of view as the battery is not absorbing some of that energy.

I don’t think the amps are directly the problem, but more to do with the frequency of the voltage spikes, it’s the magnitude and rate of rise that damages the caps/FET’s

 

A reliability issue? Not really if people don’t follow manufacturers recommendations, then they will stress the ESC to a point of failure – no surprise really. TBH I would have thought the failure would be quite quick as in seconds to minutes rather than hours or days, but I could be corrected.

Having now written this I don’t think we are to two far apart, just the root cause of the issue. The solution is a redesign as George mentioned although I suspect that and a combination of higher rated capacitors (voltage/capacity) resolve the problem.

These are my views and if you want to purchase a ESC rated for long battery/ESC leads and chat about the technicalities then George at 4-max has been very helpful in the past.

 

Hope that helps in some way ?

Link to comment
Share on other sites

This is all good background knowledge and very relevant in some installations.

 

However in specific answer to the OP's question - don't worry about it Simon and put the ESC's in the wing as you intend. In the TwinStar the runs are so comparatively short & the components lightly stressed either way is not an issue. Like Frank the ESC's in mine are in the wing and have been operating without any fuss for about 7 years.

1046885250_Twinstarmotor.thumb.jpg.b1008e5e56c664661a8d288711d28309.jpg

Link to comment
Share on other sites

Lots of interesting reading; many thanks to all who contributed.

Oddly enough I've now come to the conclusion that the best solution for me is to mount the ESC's in the fuselage. I only need to solder on some extensions from the ESC to the motor and no other mods apart from a simple wiring harness to the Rx and Battery.

 

I will also cut out an air exit hole in the bottom of the fuselage to aid cooling.

  • Sad 1
Link to comment
Share on other sites

  • 5 months later...

John

Excuse all the above comments.  

It all comes down to the rating of the brushed motor and its speed controller.

For example if it was intended to be used on 6V (5s NiMh) then a 2s LiPo (8V fully charged) is likely to both overload the speed controller and shorten the life of the motor brushes significantly.

What type and number of cells does it use at the moment?

 

My first RC plane with a 540 brushed motor on 9.6V NiMh gave up after a few flights when run on a 3s LiPo. Substituted for an equivalent brushless motor and speed controller it is still going 9 years later  

 

 

Link to comment
Share on other sites

1 hour ago, JOHN PENNY 1 said:

Can I use my brushed motors with  a3/1-3000 eco 11.1v  lipo please. I am newbie to electrics

 

You can but it will turn much quicker than on the normal 6cell Nimh cells they normally run on as the voltage is higher, and as power is basically rpm squared the amps go up too. So if it's prop'd for a 6 cell Nimh and you put a 3 cell lipo on you'll get lots more power, but maybe not for long, I did this on an old MPX Twinstar, it was great for a few flights until a motor burnt out! 

 

What motor and propellor are you using? a 2s Lipo might be a better option, unless you have a disciplined throttle thumb.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...